OSCILLATING-PLASMA GLOW-DISCHARGE AS A DETECTOR FOR GAS-CHROMATOGRAPHY

The change in frequency of a 427-kHz oscillation in the current of a glow discharge cell at 1.8 Torr is a linear and sensitive measure of organic analyte concentration in the argon plasma support gas. When the plasma cell is used as a gas chromatography detector, an injection of 3 x 10(-11) mol of propanol produces a peak signal maximum corresponding to twice the standard deviation in the background signal when 0.1-s counting times are used. Only 20 fmol is present in the apparently active region of the detector at the detection limit. The gas sample is introduced into the plasma cell in the direction of the cathode via a 0.34-mm-diameter hole in the center of the anode. The gas jet that results is surrounded near its natural outer boundary by a 0.34-cm-i.d. glass cylinder. Gentle sputtering, aided by the jet striking the curved cathode, keeps the cathode clean.